1. Field of the Invention
The present invention relates to hole saws for power driven hole sawing operation. The present invention particularly relates to a hole saw wherein the hole saw and accompanying mandrel form a single integral unit.
2. Description of the Prior Art
Hole saws conventionally in use are formed of a cylindrical cutting blade which is separately attached to a mandrel or arbor just prior to use. The mandrel shaft is inserted into the jaws of the chuck of conventional electric power drills. Such electric drills are typically equipped with a"Jacobs" three jaw chuck.
In U.S. Pat. No. 3,999,869 a hole saws arbor construction is disclosed having a longitudinally grooved shank which telescopes into an enlarged body. The longitudinal grooves form engaging surfaces for the chuck jaws of conventional electric drills. A circular hole saw blade for cutting wood, plastic or metal is manually screwed to the base of the shank just prior to use of the hole saw. A drill bit, used to start the hole, is placed within the shank core and secured thereto by a set screw. The arbor construction disclosed in this reference is designed for use in relatively small drills, e.g. drills having 1/4 inch to 1/2 inch capacity chucks.
In U.S. Pat. No. 4,148,593 a heavy duty arbor construction for hole saws is disclosed. As in U.S. Pat. No. 3,999,869 the base of the arbor is threaded so that a circular hole saw of desired diameter can be screwed to the arbor base just prior to use. The arbor, has a longitudinally grooved shaft inserted into an electric drill chuck and a quick disconnect drive collar which is slideably mounted on the shaft. After the hole saw of desired diameter is manually screwed onto the arbor base, the drive collar is manually slid down the shaft until drive pins attached to the underside of the collar engage receiving holes on the top surface of the hole saw. Engagement of the drive collar to the hole saw helps to transmit torque to the hole saw and lock up of the hole saw on the arbor during operation. The arbor design disclosed in this reference has the disadvantage that the arbor is expensive and hole saw blades must be manually attached to the arbor prior to use.
In U.S. Pat. No. 4,077,737 an integral hole saw and arbor construction is disclosed. The arbor is formed of a longitudinal shank telescoping into an intermediate drive plate which in turn telescopes into a circular end cap. The top of the end cap is permanently secured to the intermediate drive plate by a circumferential continuous tungsten inert gas (TIG) weld between the intermediate drive plate and the top surface of the end cap. (Col. 4, lines 54 to 58). The hole saw is permanently secured to the bottom of the end cap by a continuous circumferential TIG weld between the bottom of the end cap and the top surface of the cylindrical hole saw. (Col. 5, lines 3 to 9). These two welds provide the necessary strength for withstanding the high forces and stresses exerted during the hole sawing operation. (Col. 5, lines 6 to 9). A pilot drill bit is slid into the core of the arbor shaft prior to use. The drill bit is held firmly in place in the arbor shaft by a set screw which penetrates the shaft wall and connects with the drill bit. The set screw must be manually tightened.
The arbor constructions of the type disclosed in U.S. Pat. Nos. 3,999,869 and 4,148,593 have the advantage that they may be reused when the hole saw blade becomes worn. That is, the worn blade is removed from the arbor and another one secured thereto in its place. The arbor constructions, disclosed in these two references are heavy duty, permit high torque transmission and consequently allow sawing of even hard metals, e.g. metals which are not easily machined as well as soft thick metals, e.g. low carbon steel metals having thicknesses greater than 1/32 inch. The hole saw blade, however, must be separately mounted on the arbor before operation. The integral arbor construction disclosed in U.S. Pat. No. 4,077,737 has the disadvantage that two continuous welds, each at different points on the shaft, are required to complete the construction. This adds to the cost of manufacture. Also the design shown in this latter reference has the disadvantage that it requires the tightening of a set screw to hold the pilot drill in place prior to use.
Accordingly it is principal objective of the present invention to provide a one piece hole saw assembly which may be inserted into a conventional electric drill.
Another objective is to provide a hole saw assembly which is relatively inexpensive to manufacture but yet is strong enough to withstand the torsional stresses encountered during the sawing operation. A related objective is to provide a one piece hole saw assembly suitable for cutting holes in wood and metals which are easily machinable.